The following abbreviations will be referenced in the ensuing description.
APAccess PointARAccess RouterBUBinding UpdateCoACare-of AddressHAHome AgentHA_MRHome Agent Mobile RouterLLALink Layer AddressMACMedia Access ControlMNNMobile Network NodeMONETMObile NETworkMRMobile RouterPANPersonal Area NetworkPSBUPrefix Scope Binding Update
In general, network mobility support deals with managing the mobility of an entire network, viewed as a single unit, which is capable of changing its point of attachment to the Internet and thus its reachability in the Internet topology. This type of network can be referred to as a MONET, and includes at least one MR connected to the global Internet. Those nodes behind the MR, referred to as MNNs, may be fixed or mobile.
A MONET can take several different forms, examples of which include the following.
Networks attached to a PAN: A mobile phone having a cellular interface and a local interface, such as a Bluetooth™ interface, together with a Bluetooth-enabled PDA constitute a very simple instance of a mobile network. In this case the mobile phone functions as the MR that is attached to the Internet via cellular links, while the PDA functions as a MNN that is used for web browsing or running a personal web server.
Access networks deployed in public transportation: A public transportation vehicle provides Internet access to IP devices carried by passengers. The access points in the vehicle function as MRs, while the passenger's personal communication devices are MNNs.
FIG. 1 shows an example of a conventional MONET 1 and its connection to the Internet 2. The MR 3 of the MONET 1 connects to the Internet 2 via an access network 4. An AR 5 in the access network 4 is a first-hop router that connects the MR 3 to the Internet 2. At least one link technology-specific AP 6 may exist between the MR 3 and the AR 5 to provide link layer connectivity between the MR 3 and the AR 5. The MR 3 may move between APs 6 and/or ARs 5, and thus a handover mechanism is provided. A plurality of MNNs 7 (shown for convenience as three MNNs, two being mobile and one being fixed) connect to the access network 4 via the MR 3. The link technology used in the MONET 1 may or may not be the same as the link technology used between MR 3 and the AP 6. Each MNN 7 and the MR 3 may configure its own EUI-64 Link Layer Address (LLA) based on the link technology in use.
Two types of approaches can be employed to provide mobility control and address management to the MNNs 7.
A first type of approach is a NEMO technique. NEMO support requires that none of the nodes behind the MR 3 be aware of the MONET mobility. In another words, the change of attachment of the MONET 1 should be completely transparent to the MNNs 7 behind the MR 3. The NEMO technique is described in greater detail below with regard to FIG. 2.
The basic NEMO approach is illustrated in FIG. 2. The MR 3 is assumed to have an assigned home network with a home agent referred to as the HA_MR 8. Each MONET 1 where a MR 3 resides is assigned a MONET network prefix (MNP), which is the permanent network prefix assigned in the home link of the MR 3. The MNP is not changed when the MR 3 moves its network attachment from one AR 5 to another. The ingress interface of the MR 3 is configured with the MNP, and the CoAs of all the MNNs 7 in the MONET 1 are configured using the MNP. As long as the MNN 7 resides within the same MONET 1, its CoA need not be changed. The MNN 7 may update a binding cache 9 in its own HA10 and correspondent nodes 12 by sending a BU. With this configuration, all of the packets sent to the CoA of the MNN 7 are first routed to the home link of the MR 3, and intercepted by the HA_MR 8, which further routes the packet to the MR 3 as described below.
The MR 3 configures its CoA using the network prefix advertised by the serving AR 5 (AR-1) on its egress interface. When the MR 3 changes its attachment point, it reconfigures its CoA using the prefix of the new AR 5 (AR-2). In addition to sending a BU with the new CoA to the HA_MR 8 to update the binding cache 9A, the MR 3 also sends a Prefix Scope Binding Update (PS BU) message to the HA_MR 8. The PS BU is an enhanced BU that associates the CoA of the MR 3 to the MNP instead of to a single address. The HA_MR 8 uses this binding to tunnel (shown generally as tunnel 11) to the MR 3 any packet that shows the MNP in the destination field, although some other scheme (e.g., router optimization) may be used to avoid or reduce the overhead due to the tunneling between the HA_MR 8 and the MR 3. After decapsulating the tunneled packet from the HA_MR 8, the MR 3 forwards the original packet to the correspondent MNN 7 within the MONET 1.
With this approach, even when the MR 3 moves between ARs 5, and thus changes its CoA, the MNNs 7 within the MONET 1 are enabled to use the same CoA, and no new CoAs are needed for MNNs. This reduces the overhead due to IP mobility of each MNN 7. However, the overhead due to the bi-directional tunneling between the HA_MR 8 and the MR 3 is posted over the interface between the MR 3 and the AR 5, and is applied to all packets inbound to or outbound from the MNNs 7. Since the access interface between the MR 3 and the access network 4 is most likely a radio interface in the cases of particular interest to this invention, the overhead incurred by the use of the tunneling 11 significantly reduces the spectrum efficiency of the wireless link.
A second approach is a flat structure technique, where instead of providing grouped IP mobility as in the NEMO approach each MNN 7 is responsible for handling its own IP mobility. Each MNN 7 configures its associated CoA using the prefix of the serving AR 5. Whenever MR 3 attaches to a new AR 5, each MNN 7 reconfigures its CoA and sends a BU to its HA 10 and correspondent nodes. Packets flowing towards a MNN 7 are routed based on the CoA of the MNN 7 and, thus, no tunneling protocol is required between the HA_MR 8 and the MR 3 as in the NEMO approach.
Each of these two approaches may be used in different applications, and in some cases may coexist.
Although optimized for grouped mobility, the NEMO-based approach introduces a high overhead over the access interface, and a corresponding low routing efficiency, due to the tunneling 11 that occurs between the HA_MR 8 and the MR 3. The presence of the HA_MR 8 also requires infrastructure support from the service provider. The NEMO-based solution is thus more applicable to the task of providing access in a high mobility environment, such as a high speed mass transportation environment involving, for example, a train or a bus.
When compared to the NEMO approach, the flat structure approach has the advantage that it does not require the support of the HA_MR 8, and thus provides enhanced system simplicity for the service provider. It also eliminates the tunneling 11 between the MR 3 and the HA_MR 8, as well as the triangle routing introduced by the presence of HA_MR 8, and thus leads to an improved spectrum efficiency and reduced transport delay and overhead. The flat structure based solution is more applicable in a hot spot application such as is found in a small area such as an office, home, café or airport, with no or low mobility.
In the flat structure-based mobility management approach each MNN 7 sends its neighbor advertisement to the AR 5 via the MR 3. The neighbor advertisement contains the mapping between the CoA of the MNN 7 and its LLA, which is recorded in a neighbor cache of the AR 5. When the AR 5 receives a downlink packet directed toward the MNN 7, it uses the LLA recorded in the neighbor cache to transmit the layer 2 (L2) frame to the MNN 7. However, since the link technology used in the access network 4 and in the MONET 1 could be completely different, the access network 4 and the MONET 1 may have a completely different LLA management scheme. For example, the self-constructed EU-64-bit format of LLA used in Ethernet and other access technologies, may not be applicable to an access network 4 that employs cellular technology having a centralized control mechanism of LLA assignment. As a result, the LLA for each MNN 7 may not be recognized by the nodes in the access network 4, and the L2 frame sent from the AR 5 using the LLA of the MNN 7 may not reach the MONET 1.
It can thus be appreciated that in the flat structure approach to mobility control and address management discussed above, in order for the AR 5 to route the downlink packet to the MNN 7 through the corresponding MR 3, some special address management and mobility control schemes are required. However, prior to this invention a suitable-address management and mobility control scheme was not available.